Lubricants and methods to determine dewetting thickness thereof

ABSTRACT

A lubricant including a plurality of segments including a divalent center segment and two sidechain segments, each including a perfluoroalkyl ether moieties is provided in which a dewetting thickness of the lubricant may be determined based in-part on a segment weight average molecular weight of the segments. A magnetic recording medium and a magnetic data storage system including the lubricant are also provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of U.S. ProvisionalPatent Application No. 63/136,991, filed on Jan. 13, 2021 entitled,“LUBRICANTS AND METHODS TO DETERMINE DEWETTING THICKNESS THEREOF,” theentire content of which is incorporated herein by reference.

FIELD

The instant disclosure is directed to lubricants, and more particularly,to lubricants and methods for determining a dewetting thickness of thelubricants, where the lubricants are suitable for use in variousapplications, including magnetic recording media.

INTRODUCTION

The instant disclosure relates to lubricants suitable for use inmagnetic storage media, and in particular, media configured for heatassisted magnetic recording (HAMR). Magnetic storage systems, such as ahard disk drive (HDD) systems, are utilized in a wide variety of devicesin both stationary and mobile computing environments. Examples ofdevices that incorporate magnetic storage systems include data centerstorage systems, desktop computers, portable notebook computers,portable hard disk drives, network storage systems, high definitiontelevision (HDTV) receivers, vehicle control systems, cellular or mobiletelephones, television set top boxes, digital cameras, digital videocameras, video game consoles, and portable media players.

A typical disk drive includes magnetic storage media in the form of oneor more flat disks or platters. The disks are generally formed of twomain components, namely, a substrate material that gives it structureand rigidity, and a magnetic media coating that holds the magneticimpulses or moments that represent data in a recording layer within thecoating. The typical disk drive also includes a read head and a writehead, generally in the form of a magnetic transducer which can senseand/or change the magnetic fields stored on the recording layer of thedisks. HAMR is a technique that can increase the areal density (AD) ofwritten data on a magnetic storage medium having high coercivity usinghigh recording temperatures to write information to the medium. However,the high recording temperatures applied to the media may presentchallenges.

Due to the high temperatures involved, lubricants suitable for use inHAMR drives may benefit from high thermal stability. Other examples ofmagnetic storage media include flexible tape media usable for magnetictape recording. As such, there is a need in the art for lubricantshaving high thermal stability and other properties for use in HAMRdrives or in magnetic tape recording. In addition, determination of alubricant dewetting thickness and other parameters is typically done byfirst producing the lubricant and then testing the lubricant. There is aneed in the art to design and/or select lubricants having specificproperties suitable for specific uses prior to synthesizing thelubricant.

SUMMARY

In one aspect, this disclosure provides a lubricant comprising:

a plurality of segments, each linked together by ether linkage accordingto a general formula:

Re¹—Rb¹—Ri—Rc—Ri—Rb²—Re²;

wherein Rc is a divalent center segment including a perfluoroalkyl ethermoiety;

wherein each of Rb¹ and Rb² is, independently, a sidechain segmentincluding a perfluoroalkyl ether moiety;

wherein each Ri is, independently, a divalent linking segment includinga functional group including elements from Group 13-17 of the periodictable of the elements;

wherein each of Re¹ and Re² is, independently, a monovalent end segmentincluding a functional group including elements from Group 13-17 of theperiodic table of the elements;

wherein Rb¹≠Rc≠Rb²; and

wherein the lubricant comprises a segment weight average molecularweight (α) determined according to the formula:

α=[molecular weight of Rb¹+molecular weight of Rb²+molecular weight ofRc]÷3; and

a dewetting thickness T_(dw) determined according to the formula:

T _(dw)=ψ(α);

wherein ψ is a function determined from a relationship between dewettingthickness and segment weight average molecular weight of a plurality ofother lubricants;

wherein each of the plurality of other lubricants includes one or moresegments including perfluoroalkyl ether moieties;

wherein the segment weight average molecular weight of each of the otherlubricants is equal to the weight average molecular weight of the one ormore segments including perfluoroalkyl ether moieties present in therespective other lubricant; and

wherein the segment weight average molecular weight of each of theplurality of other lubricants is from about 300 g/mol to about 5,000g/mol.

In one aspect, this disclosure also provides a method to determine adewetting thickness of a lubricant, comprising the steps of:

a) generating a chemical representation of the lubricant including aplurality of segments, each linked together through an ether linkageaccording to a general formula:

Re¹—Rb¹—Ri—Rc—Ri—Rb²—Re²;

wherein Rc is a divalent center segment including a perfluoroalkyl ethermoiety;

wherein each of Rb¹ and Rb² is, independently, a sidechain segmentincluding a perfluoroalkyl ether moiety;

wherein each Ri is, independently, a divalent linking segment includinga functional group including elements from Group 13-17 of the periodictable of the elements;

wherein each of Re¹ and Re² is, independently, a monovalent end segmentincluding a functional group including elements from Group 13-17 of theperiodic table of the elements; and

wherein Rb¹≠Rc≠Rb²;

b) determining a segment weight average molecular weight (α) accordingto the formula:

α=[molecular weight of Rb¹+molecular weight of Rb²+molecular weight ofRc]÷3; and

c) determining the dewetting thickness T_(dw) of the lubricant accordingto the formula:

T _(dw)=0.0045(α)+8.0226.

In one aspect, this disclosure also provides a data storage system,comprising: at least one magnetic head; a magnetic recording mediumincluding a lubricant according one or more aspects disclosed herein; adrive mechanism for positioning the at least one magnetic head over themagnetic recording medium; and a controller electrically coupled to theat least one magnetic head for controlling operation of the at least onemagnetic head.

In one aspect, this disclosure also provides a data storage system,comprising a slider comprising at least one magnetic head and an airbearing surface (ABS), wherein a lubricant according one or more aspectsdisclosed herein is disposed on the ABS; and a magnetic recording mediumincluding a magnetic recording layer; wherein the slider is configuredto write information to the magnetic recording layer using heat assistedmagnetic recording (HAMR).

Other aspects and advantages of the present invention will becomeapparent from the following detailed description, which, when taken inconjunction with the drawings, illustrate by way of example, theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1a is a diagram schematically illustrating a data storage deviceincluding a slider and a magnetic recording medium in accordance withone aspect of the disclosure;

FIG. 1b is a side schematic view of the slider and magnetic recordingmedium of FIG. 1a in accordance with one aspect of the disclosure;

FIG. 2 is a side schematic view of a heat assisted magnetic recording(HAMR) medium including a lubricant layer in accordance with one aspectof the disclosure;

FIG. 3a is a schematic drawing showing a lubricant in accordance withone aspect of the disclosure;

FIG. 3b is a schematic drawing showing another lubricant in accordancewith one aspect of the disclosure;

FIG. 4 is a graph showing a plot of dewetting thickness versus a segmentweight average molecular weight of a plurality of other lubricants inaccordance with one aspect of the disclosure;

FIG. 5 is a flowchart of a method for determining a dewetting thicknessof a lubricant in accordance with one aspect of the disclosure; and

FIG. 6 is a flowchart of a method for forming a magnetic recordingmedium having a lubricant layer thereon, in accordance with one aspectof the disclosure.

DETAILED DESCRIPTION

Dewetting thickness of lubricants utilized on magnetic recording mediais known to affect a variety of properties of the lubricant layerincluding the average thickness of the lubricant layer, the siloxanecontamination robustness of the media provided by the lubricant, thehead wear characteristics of a data storage system including magneticrecording media having the lubricant, and a number of other properties.The dewetting thickness of lubricants was previously determinedexperimentally. In one aspect, this disclosure relates to a lubricant inwhich a dewetting thickness T_(dw) of the lubricant may be determinedaccording to a formula, which relates dewetting thickness to a segmentweight average molecular weight of the lubricant. The dewettingthickness formula may be determined from a relationship betweendewetting thickness data of other previously known lubricants and thesegment weight average molecular weight of these known lubricants. Inone aspect, the T_(dw) of the lubricant may be determined by a linearfit of dewetting thickness to a segment weight average molecular weightof the other lubricants. In one aspect, this disclosure involves amethod to determine a dewetting thickness of a lubricant that includesthe steps of (1) providing a representation of the lubricant, e.g., thechemical formula of a proposed or possible lubricant, (2) determiningthe segment weight average molecular weight of this lubricant from thechemical formula, followed by (3) determining the dewetting thickness ofthe lubricant according to the dewetting thickness formula. In turn, alubricant may be designed and/or selected according to its structure topossess a dewetting thickness within a particular range. This may bedone instead of having to produce multiple lubricants and determine bytrial and error which is suitable for a particular purpose as is commonin the art. The ability to predict a dewetting thickness may beparticularly useful in developing or improving HAMR media or HAMRstorage systems due to the high temperatures and other challengesassociated with such media and systems.

Definitions

For purposes herein, and the claims thereto, the new numbering schemefor the Periodic Table Groups is used as described in Chemical andEngineering News, 63(5), pg. 27 (1985). Therefore, a “group 4 metal” isan element from group 4 of the Periodic Table, e.g. Hf, Ti, or Zr. Forpurposes herein, molecular weight refers to weight average molecularweight (Mw) and is expressed as grams per mole (g/mol) unless otherwisespecified.

As used herein, and unless otherwise specified, the term “C_(n)” meanshydrocarbon(s) having n carbon atom(s) per molecule, where n is apositive integer. Likewise, a “C_(m)-C_(y)” group or compound refers toa group or compound comprising carbon atoms at a total number thereof inthe range from m to y. Thus, a C₁-C₄ alkyl group refers to an alkylgroup that includes carbon atoms at a total number thereof in the rangeof 1 to 4, e.g., 1, 2, 3 and 4.

The term “moiety” refers to one or more covalently bonded atoms whichform a part of a molecule. The terms “group,” “radical,” “moiety”, and“substituent” may be used interchangeably.

The terms “hydrocarbyl radical,” “hydrocarbyl group,” or “hydrocarbyl”may be used interchangeably and are defined to mean a group consistingof hydrogen and carbon atoms only. Preferred hydrocarbyls are C₁-C₂₀radicals that may be linear, branched, or cyclic, and when cyclic,aromatic or non-aromatic. Examples of such radicals include, but are notlimited to, alkyl groups such as methyl, ethyl, n-propyl, isopropyl,n-butyl, isobutyl, sec-butyl, tert-butyl, pentyl, iso-amyl, hexyl, octylcyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cyclooctyl, and thelike, aryl groups, such as phenyl, benzyl naphthyl, and the like.

For purposes herein, a heteroatom is any non-carbon atom, selected fromgroups 13 through 17 of the periodic table of the elements. In one ormore aspects, heteroatoms are non-metallic atoms selected from B, N, O,Si, P, S, As Se, Te and the halogens F, Cl, Br, I, and At.

Unless otherwise indicated, the term “substituted” means that at leastone hydrogen atom has been replaced with at least one non-hydrogen atomor a functional group.

For purposes herein, a functional group includes one or more of ahydrocarbyl group, a heteroatom, or a heteroatom containing group, suchas halogen (such as Br, Cl, F or I) or at least one functional groupsuch as —NR*₂, —NR*—CO—R*, —OR*, *—O—CO—R*, —CO—O—R*, —SeR*, —TeR*,—PR*₂, —PO—(OR*)₂, —O—PO—(OR*)₂, —AsR*₂, —SbR*₂, —SR*, —SO₂—(OR*)₂,—BR*₂, —SiR*₃, —(CH₂)q-SiR*₃, or a combination thereof, where q is 1 to10 and each R* is independently hydrogen, a hydrocarbyl or halocarbylradical, and two or more R* may join together to form a substituted orunsubstituted completely saturated, partially unsaturated, or aromaticcyclic or polycyclic ring structure, or where at least one heteroatomhas been inserted within a hydrocarbyl ring.

In one or more aspects, functional groups may include: a saturatedC₁-C₂₀ radical, an unsaturated C₁-C₂₀ radical, an alicyclic C₃-C₂₀radical, a heterocyclic C₃-C₂₀ radical, an aromatic C₅-C₂₀ radical, aheteroaromatic C₅-C₂₀ radical, a cyclotriphosphazine radical, a halogen,—NR*₂, —NR*—CO—R*, —OR*, —O—CO—R*, —CO—O—R*, —SeR*, —TeR*, —PR*₂,—PO—(OR*)₂, —O—PO—(OR*)₂, —N═P(NR*₂)₃, —AsR*₂, —SR*, —SO₂—(OR*)₂, —BR*₂,—SiR*₃, —(CH₂)q-SiR*₃, —(CF₂)q-SiR*₃, or a combination thereof, whereinq is 1 to 10 and each R* is, independently a hydrogen, a halogen, asaturated, unsaturated, aromatic, and/or heterocyclic C₁-C₂₀ radical.

For purposes herein, a functional group, which is attachable to asurface of a magnetic recording medium, refers to functional groupshaving increased affinity for that surface relative to the affinity ofperfluoroalkyl ethers to that same surface. Increased affinity mayinclude Van der Walls forces, weak London Dispersion forces,dipole-dipole forces, and/or the like, and/or one or more types of bondsand/or dative bonds with the surface of the magnetic recording media,preferably with a protective overcoat of a recording media. In one ormore aspects, a functional group which is attachable to a surface of amagnetic recording medium refers to functional groups having increasedaffinity for the carbon overcoat (COC) layer of the magnetic recordingmedia, relative to the affinity of perfluoroalkyl ethers to that samesurface.

A heterocyclic ring, also referred to herein as a heterocyclic radical,is a ring having a heteroatom in the ring structure as opposed to aheteroatom substituted ring where a hydrogen on a ring atom is replacedwith a heteroatom. For example, tetrahydrofuran is a heterocyclic ringand 4-N,N-dimethylamino-phenyl is a heteroatom substituted ring. Asubstituted heterocyclic ring is a heterocyclic ring where a hydrogen ofone of the ring atoms is substituted, e.g., replaced with a hydrocarbyl,or a heteroatom containing group.

A “compound” refers to a substance formed by the chemical bonding of aplurality chemical elements. A “derivative” refers to a compound inwhich one or more of the atoms or functional groups of a precursorcompound have been replaced by another atom or functional group,generally by means of a chemical reaction having one or more steps.

For purposes herein, unless otherwise specified, the lubricants includea plurality of segments and each segment is attached to the othersegment by an ether bond, e.g., a —C—O—C— linkage. For purposes herein,a segment including a perfluoropolyalkyl ether moiety has the generalformula:

—(CF₂)_(a)O—;

wherein each a is from 1 to 10. A segment including a perfluoroalkylether moiety has the general formula:

—((CF₂)_(a)O)_(b)—;

wherein each a is from 1 to 10 and b is the number of repeating units inthe segment.

The perfluoroalkyl ether moieties present in a particular segment arebonded together to form a perfluoropolyalkyl ether chain. Unlessindicated otherwise, each of the perfluoroalkyl ether moieties presentin a perfluoropolyalkyl ether segment may be the same or different. Forexample, the following are each examples of a perfluoropolyalkyl ethersegments:

i) —(CF₂CF₂O)_(b)—, a perfluoropolyethylether segment;

ii) —(CF₂CF₂CF₂O)_(b)—, a perfluoropolypropylether segment;

iii) —(CF₂CF₂CF₂CF₂O)_(b)—, a perfluoropolybutylether segment; and

iv) —(CF₂CF₂O)_(b)—(CF₂O)_(b′)—, aperfluoropolyethylether-perfluoropolymethylether segment, also referredto in the art as a Z-chain segment.

For purposes herein, the molecular weight of a segment, e.g., a divalentcenter segment including a perfluoroalkyl ether moiety Rc and/or adivalent sidechain segment including a perfluoroalkyl ether moiety Rb¹and Rb² is defined as the molecular weight of the perfluoroalkyl ethermoieties present in the segment.

Unless otherwise indicated, a divalent center segment, abbreviated Rcherein, refers to a divalent chemical moiety including a perfluoroalkylether moiety, or which is formed from one or more perfluoroalkyl ethermoieties, that is chemically bonded via an ether linkage to a linkingsegment moieties on either side.

An intermediate or linking segment, abbreviated as Ri herein, refers toa chemical moiety bonded between the center segment and a sidechainsegment by an ether linkage, and which includes at least one functionalgroup, which is preferably selected to attached to the protective layerof the magnetic recording media.

A side chain segment, abbreviated Rb herein, refers to a divalentchemical moiety including a perfluoroalkyl ether moiety, or formed fromone or more perfluoroalkyl ether moieties, that is chemically bonded viaan ether linkage to a linking segment moiety and an end segment.

An end segment, abbreviated Re herein, refers to a mono-valent radicalwhich includes at least one functional group preferably selected toattached to the protective layer of the magnetic recording media. Theend moieties are located at either end of a sidechain of the lubricantmolecule.

For any particular compound disclosed herein, any general or specificstructure presented also encompasses all conformational isomers,regio-isomers, and stereoisomers that may arise from a particular set ofsubstituents, unless stated otherwise. Similarly, unless statedotherwise, the general or specific structure also encompasses allenantiomers, diastereomers, and other optical isomers whether inenantiomeric or racemic forms, as well as mixtures of stereoisomers, aswould be recognized by a skilled artisan.

As used herein, the term “aromatic” also refers to pseudoaromaticheterocycles which are heterocyclic substituents that have similarproperties and structures (nearly planar) to aromatic heterocyclicligands, but are not by definition aromatic; likewise the term aromaticalso refers to substituted aromatics.

As used herein, a moiety which is chemically identical to another moietyis defined as being identical in overall composition exclusive ofisotopic abundance and/or distribution, and/or exclusive ofstereochemical arrangement such as optical isomers, confirmationalisomers, spatial isomers, and/or the like.

Data Storage Device

FIG. 1a is a top schematic view of a data storage device 100 (e.g., diskdrive or magnetic recording device) configured for heat assistedmagnetic recording (HAMR) including a slider 108 and a magneticrecording medium 102 having a lubricant layer according to one or moreaspects of the disclosure. The laser (not visible in FIG. 1a but see 114in FIG. 1b ) is positioned with a head/slider 108. Disk drive 100 mayinclude one or more disks/media 102 to store data. Disk/media 102resides on a spindle assembly 104 that is mounted to a drive housing.Data may be stored along tracks in the magnetic recording layer of disk102. The reading and writing of data is accomplished with the head 108(slider) that may have both read and write elements (108 a and 108 b).The write element 108 a is used to alter the properties of the magneticrecording layer of disk 102 and thereby write information thereto. Inone aspect, head 108 may have magneto-resistive (MR), giantmagneto-resistive (GMR), or tunnel magneto-resistive (TMR) elements. Inan alternative aspect, head 108 may be another type of head, forexample, a Hall effect head. In operation, a spindle motor (not shown)rotates the spindle assembly 104, and thereby rotates the disk 102 toposition the head 108 at a particular location along a desired disktrack 107. The position of the head 108 relative to the disk 102 may becontrolled by the control circuitry 110 (e.g., a microcontroller). It isnoted that while an example HAMR system is shown, the variousembodiments described may be used in other EAMR or non-EAMR magneticdata recording systems, including perpendicular magnetic recording (PMR)disk drives or magnetic tape drives.

FIG. 1b is a side schematic view of the slider 108 and magneticrecording medium 102 of FIG. 1 a. The magnetic recording medium 102includes a lubricant layer (see FIG. 3) in accordance with one or moreaspects of the disclosure. The slider 108 may include a sub-mount 112attached to a top surface of the slider 108. The laser 114 may beattached to the sub-mount 112, and possibly to the slider 108. Theslider 108 includes a write element (e.g., writer) 108 a and a readelement (e.g., reader) 108 b positioned along an air bearing surface(ABS) 108 c of the slider for writing information to, and readinginformation from, respectively, the media 102. In other aspects, theslider may also include a layer of the lubricant (not shown).

In operation, the laser 114 is configured to generate and direct lightenergy to a waveguide (e.g., along the dashed line) in the slider whichdirects the light to a near field transducer (NFT) near the air bearingsurface (e.g., bottom surface) 108 c of the slider 108. Upon receivingthe light from the laser 114 via the waveguide, the NFT generateslocalized heat energy that heats a portion of the media 102 within ornear the write element 108 a, and near the read element 108 b. Theanticipated recording temperature is in the range of about 350° C. to400° C. In the aspect illustrated in FIG. 1B, the laser directed lightis disposed within the writer 108 a and near a trailing edge of theslider. In other aspects, the laser directed light may instead bepositioned between the writer 108 a and the reader 108 b. FIGS. 1A and1B illustrate a specific example of a HAMR system. In other examples,the magnetic recording medium 102 with the lubricant layer according toaspects of the disclosure can be used in other suitable HAMR systems(e.g., with other sliders configured for HAMR).

Magnetic Recording Medium

FIG. 2 is a side schematic view of a magnetic recording medium 200having a lubricant layer according to one or more aspects of thedisclosure. In one aspect, the magnetic recording medium 200 may be usedin a data storage system configured for HAMR (e.g., disk drive 100). Themagnetic recording medium 200 has a stacked structure with a substrate202 at a bottom/base layer, an adhesion layer 204 on the substrate 202,a heat sink layer 206 on the adhesion layer 204, an interlayer 208 onthe heat sink layer 206, a magnetic recording layer (MRL) 210 on theinterlayer 208, a capping layer 212 on the MRL 210, an overcoat layer214 on the capping layer 212, and a lubricant layer 216 on the overcoatlayer 214. In one aspect, the magnetic recording medium 200 may have asoft magnetic underlayer (SUL) between the adhesion layer 204 and theheat sink layer 206. In one aspect, the magnetic recording medium 200may have a thermal resistance layer (TRL) between the interlayer 208 andthe heat sink layer 206. In one aspect, for disk drive applications, thesubstrate 202 can be made of one or more materials such as an Al alloy,NiP plated Al, glass, glass ceramic, and/or combinations thereof. In oneaspect for magnetic tape recording applications, the substrate 202 caninclude a flexible material, such a film made of one of various types ofresins, polyesters, polyolefins, polyamides, and the like, orcombinations thereof. The substrate may include non-magnetic materials,and may be laminated. In some aspects, the magnetic recording medium 200may have some or all of the layers illustrated in FIG. 2 and/oradditional layer(s) in various stacking orders. It should also be notedthat each layer shown in FIG. 2 may include one or more sub-layers. Forexample, the magnetic recording layer may comprise multiple layers incertain embodiments.

Lubricants

In one aspect, lubricants according to aspects disclosed herein mayfunction as boundary lubricants which may be used in various mechanicaldevices, including data storage systems configured for magneticrecording (e.g., hard disk drives or tape drives) and othermicroelectronic mechanical systems. Boundary lubricants may form alubricant layer when one or more functional groups of the lubricantattach or otherwise engage with the surface being lubricated. Forinstance, one or more boundary lubricants may form a lubricant layer 216on a magnetic recording medium 200 (e.g. a disk that includes a magneticrecording layer 210) that moves relative to other parts in themechanical device. This lubricant layer 216 may help to protect themagnetic recording medium from frictional wear and/or damage caused byinteractions between the magnetic recording medium and other parts inthe mechanical device (e.g., interactions, such as contact, between aslider and the magnetic recording medium). In other words, this boundarylayer may help limit or minimize solid-to-solid contact.

FIG. 3a illustrates an exemplary boundary lubricant (Example 1,generally indicated as 300), according to one aspect of the disclosureboth as a figure and the corresponding chemical formula. As shown inFIG. 3a , the Example 1 boundary lubricant 300 includes a plurality ofsegments, each linked together through an ether linkage according to ageneral formula:

Re¹—Rb¹—Ri—Rc—Ri—Rb²—Re²;

wherein Rc is a divalent center segment 302 including a perfluoroalkylether moiety; Rb¹ is a first sidechain segment 306, Rb² is a secondsidechain segment 306′, each independently includes a perfluoroalkylether moiety; each Ri segment is, independently, a divalent linkingsegment 304 including a functional group including elements from Group13-17 of the periodic table of the elements, which in this aspect arehydroxyl groups (—OH). Re¹ is a first end segment 308 and Re² is secondend segment 308′, each is a monovalent end segment including afunctional group including elements from Group 13-17 of the periodictable of the elements, which in this aspect are hydroxyl groups (—OH).As shown in FIG. 3a , Rb¹≠Rc≠Rb² and Rb¹=Rb².

In the aspect shown in FIG. 3a , each of the sidechain segments 306includes a perfluoroethyl ether moiety —(CF₂CF₂O)_(b)— where b is 6,e.g., b¹ and b² shown in FIG. 3a , and the center segment 302 includes aperfluoroethyl ether moiety —(CF₂CF₂O)_(b)— where b is 2, e.g., b³ shownin FIG. 3a . Each of the linking segments 304 includes a hydroxylfunctional group, along with the end groups Re¹ (308) and Re² (308′),which are selected for the ability to attach to the surface of thecarbon overcoat of the recording media, due in part to being highlypolar moieties.

FIG. 3b illustrates another exemplary boundary lubricant (Example 2,generally indicated as 310), according to another aspect of thedisclosure both as a figure and the corresponding chemical formula. Asshown in FIG. 3b , the Example 2 boundary lubricant 310 includes aplurality of segments, each linked together through an ether linkageaccording to a general formula:

Re¹—Rb¹—Ri—Rc—Ri—Rb²—Re²;

wherein Rc is a divalent center segment 312 including a perfluoroalkylether moiety; Rb¹ is a first sidechain segment 316, Rb² is a secondsidechain segment 316′, each independently includes a perfluoroalkylether moiety; each Ri segment is, independently, a divalent linkingsegment 314 including a functional group including elements from Group13-17 of the periodic table of the elements, which in this aspect arehydroxyl groups (—OH). Re¹ is a first end segment 318 and Re² is secondend segment 318′, each is a monovalent end segment including afunctional group including elements from Group 13-17 of the periodictable of the elements, which in this aspect are hydroxyl groups (—OH).In this aspect of the disclosure, Rb¹≠Rc≠Rb², and Rb¹=Rb².

In the aspect shown in FIG. 3b , each of the sidechain segments 316includes a perfluoroethyl ether moiety —(CF₂CF₂O)_(b)— where b is 2,e.g., b¹ and b² shown in FIG. 3b , and the center segment 312 includes aperfluoroethyl ether moiety —(CF₂CF₂O)_(b)— where b is 6, e.g., b³ shownin FIG. 3b . Each of the linking segments 314 along with the end groupsRe¹ (318) and Re² (318′) include a functional group, which in thisaspect are hydroxyl groups (—OH).

Method to Determine Dewetting Thickness

Table 1 (shown below) presents the dewetting thickness and segmentweight average molecular weight data obtained from a plurality of otherlubricants. Each of the other lubricants includes at least one segmentincluding perfluoroalkyl ether moieties linked to other segments throughan ether linkage which include a functional group including elementsfrom Group 13-17 of the periodic table of the elements. Some of theother lubricants of Table 1 include a divalent center segment Rc′including perfluoroalkyl ether moieties terminated by monovalent endsegments Re^(1′) and Re^(2′) including a functional group includingelements from Group 13-17 of the periodic table of the elements, e.g.,according to the general formula:

Re^(1′)—Rc′—Re^(2′).

Other lubricants used to produce Table 1 include a plurality ofsegments, each linked together through an ether linkage according to ageneral formula:

Re—Rb—Ri—Rc—Ri—Rb—Re;

wherein Rc is a divalent center segment including a perfluoroalkyl ethermoiety; each Rb is a sidechain segment that includes a perfluoroalkylether moiety; the Ri segments are divalent linking segments including afunctional group including elements from Group 13-17 of the periodictable of the elements, and Re is a monovalent end segment including afunctional group including elements from Group 13-17 of the periodictable of the elements.

TABLE 1 Segment Weight Average Molecular Weight and Dewetting Thicknessof known lubricants Table 1 Segment Weight Average Dewetting ThicknessT_(dw) Molecular Weight α g/mol (Å) 1500 16.6 2210 18.4 3390 23.5 382025.2 2210 19.3 2240 15.9 1290 11.5 1290 12.6 4200 26.9 408 8 872 12.5640 15 930 11

A plot of the data presented in Table 1 is shown in FIG. 4. Applicanthas discovered that a dewetting thickness T_(dw) of a lubricant may bedetermined according to the formula:

T _(dw)=ψ(α);

in which α is the segment weight average molecular weight of thelubricant, and ψ is a function determined from a relationship betweendewetting thickness and segment weight average molecular weight of aplurality of other lubricants; wherein each of the plurality of otherlubricants independently includes a center segment and/or sidechainsegments including perfluoroalkyl ether moieties. In one aspect, ψ is afunction determined from a relationship between dewetting thickness andsegment weight average molecular weight of a plurality of otherlubricants, wherein each of the plurality of other lubricants includesone or more segments including perfluoroalkyl ether moieties, whereinthe segment weight average molecular weight of each of the otherlubricants is equal to the weight average molecular weight of the one ormore segments including perfluoroalkyl ether moieties present in therespective other lubricant, and wherein the segment weight averagemolecular weight of each of the plurality of other lubricants is fromabout 300 g/mol to about 5,000 g/mol.

In one aspect, the function ψ is a linear fit of dewetting thicknessversus segment weight average molecular weight of a plurality of theother lubricants. In one aspect the relationship may be determinedaccording to a linear fit of these data, while in other aspects othermathematical fits or relationships may be utilized.

In the exemplary aspect of the disclosure shown in FIG. 4, the functionψ(α) is produced from a least squares fit of the dewetting thicknessversus the segment weight average molecular weight of a plurality of theother lubricants, which resulted in an essentially linear relationship.A least squares linear fit of these data (as is known in the art)resulted in the equation T_(dw)=ψ(α) being equal toT_(dw)=0.0045α+8.0226, with an R² fit of 0.9035.

Referring to FIG. 5, a method 500 for determining a dewetting thicknessof a lubricant is shown according to one aspect of the disclosure. Asshown in FIG. 5, the method 500 includes providing a representation ofthe lubricant including a plurality of segments, each linked togetherthrough an ether linkage according to a general formula:

Re¹—Rb¹—Ri—Rc—Ri—Rb²—Re²;

wherein Rc is a divalent center segment including a perfluoroalkyl ethermoiety;

wherein each of Rb¹ and Rb² is, independently, a sidechain segmentincluding a perfluoroalkyl ether moiety;

wherein each Ri is, independently, a divalent linking segment includinga functional group including elements from Group 13-17 of the periodictable of the elements; and

wherein each of Re¹ and Re² is, independently, a monovalent end segmentincluding a functional group including elements from Group 13-17 of theperiodic table of the elements; and wherein Rb¹≠Rc≠Rb2. See operation502.

The method 500 further includes determining a segment weight averagemolecular weight (α) according to the formula:

α=[molecular weight of Rb¹+molecular weight of Rb²+molecular weight ofRc]÷3.

See operation 504.

In various approaches, the method 500 further includes determining adewetting thickness T_(dw) determined according to the formula:

T _(dw)=ψ(α);

wherein ψ is a function determined from a relationship between dewettingthickness and a segment weight average molecular weight of a pluralityof other lubricants, each of the plurality of other lubricantsindependently including a center segment and/or sidechain segmentsincluding perfluoroalkyl ether moieties. In one aspect, ψ is a functiondetermined from a mathematical fit, e.g., a linear fit of datarepresenting dewetting thickness and segment weight average molecularweight of a plurality of other lubricants. For example, utilizing theequation determined in FIG. 4, such that the method includes determiningthe dewetting thickness T_(dw) of the lubricant according to theformula: T_(dw)=0.0045(α)+8.0226. See operation 506, as shown in FIG. 5.

Returning to FIGS. 3a, and 3b , the segment weight average molecularweight (α) of these exemplary aspects of the disclosure is equal to thesum of the molecular weight of Rb¹+molecular weight of Rb²+molecularweight of Rc; divided by 3. The molecular weight of each perfluoroethylether moiety is 116.015 g/mol. Accordingly, the segment weight averagemolecular weight (α) of the aspect of the disclosure indicated asExample 1 (300) in FIG. 3a is:

α=(116.015*b ¹+116.015*b ²+116.015*b ³)÷3;   Example 1

α=(116.015*6+116.015*6 +116.015*2)÷3;   Example 1

α=(1624.21)÷3;   Example 1

α=541.40.   Example 1

Likewise, the segment weight average molecular weight (α) of the Example2 aspect of the disclosure indicated as 310 in FIG. 3b is:

α=(116.015*b ¹+116.015*b ²+116.015*b ³)÷3;   Example 2

α=(116.015*2+116.015*2 +116.015*6)÷3;   Example 2

α=(1160.15)÷3;   Example 2

α=386.71.   Example 2

Utilizing this relationship, the dewetting thickness of the exemplarylubricant Example 1 shown in FIG. 3a may be calculated as follows:

T _(dw)=0.0045α+8.0226;   Example 1

T _(dw)=0.0045*541.40+8.0226;   Example 1

T_(dw)=10.46 Å.   Example 1

The same calculation of the dewetting thickness of the exemplarylubricant Example 2 shown in FIG. 3b results in a dewetting thickness of9.76 Å. These data are shown in Table 2 along with the measureddewetting thickness of the two exemplary lubricants.

TABLE 2 Segment Calculated Measured Weight Average Dewetting DewettingMolecular Thickness Thickness Example Weight α (g/mol) Tdw (Å) Tdw (Å)Uncertainty EXAMPLE 1 541.40 10.46 10.9 +/−0.4 Å EXAMPLE 2 386.71 9.7610.1 +/−0.2 Å

As these data show, a method according to one aspect of the disclosureprovides a determination of the dewetting thickness of a lubricantwithin +/−0.5 Å. In one aspect of the disclosure, the dewettingthickness T_(dw) may be determined according to the formula:

T _(dw)=ψ(α);

wherein ψ is function determined from a plot or other means of fittingdata to an equation (e.g., a linear fit) of dewetting thickness to asegment weight average molecular weight of a plurality of otherlubricants, each of the plurality of other lubricants independentlyincluding a center segment and/or sidechain segments includingperfluoroalkyl ether moieties, is about equal to a measured dewettingthickness of the lubricant. In one aspect of the disclosure, thedewetting thickness T_(dw) may be determined according to the formula:

T _(dw)=(α);

and is equal to a measured dewetting thickness of the lubricant +/−about 10 Å, or about 5 Å, or about 1 Å, or about 0.5 Å.

In one aspect of the disclosure, a method to determine a dewettingthickness of a lubricant includes the steps of providing arepresentation of the lubricant including a plurality of segments, eachlinked together through an ether linkage according to a general formula:

Re¹—Rb¹—Ri—Rc—Ri—Rb²—Re²;

wherein Rc is a divalent center segment including a perfluoroalkyl ethermoiety; each of Rb¹ and Rb² is, independently, a sidechain segmentincluding a perfluoroalkyl ether moiety; each Ri is, independently, adivalent linking segment including a functional group including elementsfrom Group 13-17 of the periodic table of the elements; and each of Re¹and Re² is, independently, a monovalent end segment including afunctional group including elements from Group 13-17 of the periodictable of the elements, wherein Rb¹≠Rc≠Rb². It is to be understood thatin one aspect of the disclosure, this step of providing, or generating,a representation of the lubricant only requires providing/generating thechemical formula of the lubricant, and does not necessarily requireproviding the lubricant in physical form. This allows for a lubricantaccording to the general formula to be evaluated and/or designed toinclude a particular properties as may be needed for an intended use.

The method further includes determining a segment weight averagemolecular weight (α) of the provided chemical formula according to theformula:

α=[molecular weight of Rb¹+molecular weight of Rb²+molecular weight ofRc]÷3,

followed by determining the dewetting thickness T_(dw) of the lubricantaccording to the formula:

T _(dw)=ψ(α);

wherein ψ is function determined a linear fit of dewetting thickness toa segment weight average molecular weight of a plurality of otherlubricants, each of the plurality of other lubricants independentlyincluding a center segment and/or sidechain segments includingperfluoroalkyl ether moieties.

Aspects of Lubricants

In one aspect of the disclosure, the lubricant includes or is formedfrom (e.g., comprises, consists essentially of, or consists of) aplurality of segments, each linked together through an ether linkageaccording to a general formula:

Re¹—Rb¹—Ri—Rc—Ri—Rb²—Re²;

wherein Rc is a divalent center segment including a perfluoroalkyl ethermoiety; each of Rb¹ and Rb² is, independently, a sidechain segmentincluding a perfluoroalkyl ether moiety; each Ri is, independently, adivalent linking segment including a functional group including elementsfrom Group 13-17 of the periodic table of the elements; and each of Re¹and Re² is, independently, a monovalent end segment including afunctional group including elements from Group 13-17 of the periodictable of the elements, wherein Rb¹≠Rc≠Rb².

In one aspect of the disclosure the center segment of the lubricant, Rcincludes a perfluoroethyl ether moiety and/or each of the sidechainsegments Rb¹ and Rb² includes a perfluoroethyl ether moiety.

In one aspect of the disclosure, each linking segment Ri has the generalformula:

wherein each R¹ is, independently, a functional group including elementsfrom Group 13-17 of the periodic table of the elements.

In one aspect of the disclosure, end segment Re¹ has the generalformula:

and

Re² has the general formula:

wherein each R¹ is, independently, a functional group including elementsfrom Group 13-17 of the periodic table of the elements. The differencebetween Re¹ and Re² being the additional oxygen atom required to producean ether linkage between the sidechain segment Rb¹, which begins with acarbon atom.

In some aspects, each R¹ is, independently, a functional group whichincludes: a saturated C₁-C₂₀ radical, an unsaturated C₁-C₂₀ radical, analicyclic C₃-C₂₀ radical, a heterocyclic C₃-C₂₀ radical, an aromaticC₅-C₂₀ radical, a heteroaromatic C₅-C₂₀ radical, a cyclotriphosphazineradical, a halogen, —NR*₂, —NR*—CO—R*, —OR*, —O—CO—R*, —CO—O—R*, —SeR*,—TeR*, —PR*₂, —PO—(OR*)₂, —O—PO—(OR*)₂, —N═P(NR*₂)₃, —AsR*₂, —SR*,—SO₂—(OR*)₂, —BR*₂, —SiR*₃, —(CH₂)q-SiR*₃, —(CF₂)q-SiR*₃, or acombination thereof, wherein q is 1 to 10 and each R* is, independentlya hydrogen, a halogen, a saturated, unsaturated, aromatic, and/orheterocyclic C₁-C₂₀ radical, and wherein two or more R* may jointogether to form a ring structure, and wherein at least one functionalgroup is selected to be attachable to the protective overcoat of themagnetic recording media. In some aspects of the disclosure each R¹ is ahydroxyl (—OH).

In one aspect of the disclosure, Rc is of the formula:

Rb¹ is of the formula:

and

Rb² is of the formula:

wherein each of x, y¹ and y² is, independently, an integer from 1 to 10,wherein y¹≠x≠y². This results in an asymmetric arrangement of thelubricant segments in that all of the perfluoroalkyl ether segments arenot identical. In one aspect of the disclosure, x is less than y¹ and xis less than y². In another aspect of the disclosure, x is greater thany¹ and x is greater than y². In some aspects of the disclosure, y¹≠y²,and in other aspects of the disclosure, y¹=y².

In one aspect of the disclosure the lubricant is of the general formula:

wherein each of x, y¹, and y² is an integer from 1 to 10, or from 2 to8, or from 3 to 6; subject to the proviso that y¹≠x≠y².

In one aspect of the disclosure, the dewetting thickness Tdw isaccording to the formula:

T _(dw)=0.0045(α)+8.0226; wherein

α=(116.015*y ¹+116.015*y ²+116.015*x)÷3.

In one aspect of the disclosure, the lubricant has a weight averagemolecular weight of greater than or equal to about 1 kiloDalton (kDa),or from about 1 to about 20 kDa, or from about 2 to about 10 kDa, orfrom about 3 to about 7 kDa, or from about 1 to about 5 kDa, or 2 toabout 4 kDa. In one or more aspects, the lubricants are essentially purecompounds, having a polydispersity, defined as the number averagemolecular weight Mn divided by the weight average molecular weight Mw(Mn/Mw) from about 1 to 2, or from about 1 to about 1.5, or from about 1to about 1.05.

Fabrication of Magnetic Recording Media

Applicant has discovered that a relatively high molecular weight, e.g.,greater than or equal to about 1000 atomic mass units (amu), orpreferably greater than or equal to about 3000 amu, is less prone toevaporation, which is of particular importance under the relatively hightemperature conditions used within HAMR drives. Applicant has furtherdiscovered that the induced asymmetry present in the molecular structureallows the use of the segment weight average molecular weight of themain chain segments, e.g., the center segment and the two sidechainsegments, to impart flexibility to tune the dewetting thickness of thelubricant. The accuracy of the ability to determine the dewettingthickness of a lubricant increases when the perfluoroalkyl ethersegments are formed from perfluoroethyl ether moieties. The lubricantsaccording to one or more aspects of the disclosure include enhancedadsorption, reduced lube pickup, and a reduction in the layer thicknessrequired in combination with an improved coverage. Lubricants accordingto aspects of the disclosure thus allow for operation of the head closerto the media, using a minimal lubricant thickness set according to thedewetting thickness of the lubricant. This reduces the number ofavailable sites that are prone to contamination, and renders thelubricant layer more robust while improving head wear of the magneticmedia utilizing the lubricant.

In one or more aspects, the average thickness of the lubricant layer ofthe magnetic recording medium is less than about 3 nanometers, or lessthan about 2 nm, or less than about 1 nm, or less than or equal to about0.8 nm. In some aspects, the lubricant of the magnetic recording mediumhas an average thickness from about 0.3 nm to about 3 nm, or from about0.3 to about 1 nm.

In one or more aspects of the magnetic recording medium, the lubricanthas a bonding percentage of at least 70%, or at least 75%, or at least80%, or at least 85%, corresponding to a degree of bonding of thelubricant to the total area of an upper surface of the protectiveovercoat or other surface on which the lubricant is located.

In one aspect, a magnetic data storage system includes a magnetic head;a magnetic recording medium according to any one or a combination ofaspects disclosed herein including a lubricant according to one or moreaspects disclosed herein, a drive mechanism for positioning the magnetichead over the magnetic recording medium; and a controller electricallycoupled to the magnetic head for controlling operation of the magnetichead.

Referring to FIG. 6, a method 600 for forming a magnetic recordingmedium having a boundary lubricant is shown according to one aspect ofthe disclosure. In one aspect, method 600 can be used to fabricate anyof the media shown in FIGS. 1 a, 1 b, 2. As shown in FIG. 6, the method600 includes forming a magnetic recording layer on a non-magneticsubstrate. See operation 602. In various approaches, the method 600 mayalso include forming other layers positioned between the non-magneticsubstrate and the magnetic recording layer. These other layers mayinclude, for example, one or more underlayers, soft underlayers,adhesion layers, etc. (e.g., any of the layers shown in FIG. 2). As alsoshown in FIG. 6, the method 600 further includes forming a protectiveovercoat above the magnetic recording layer and/or forming a cappinglayer on the magnetic layer and forming a protective overcoat layer onthe capping layer. See operation 604. The method 600 further includesforming a lubricant layer on the protective overcoat layer. Seeoperation 606. This lubricant layer may include a lubricant including aplurality of segments, each linked together through an ether linkageaccording to a general formula:

Re¹—Rb¹—Ri—Rc—Ri—Rb²—Re²;

wherein Rc is a divalent center segment including a perfluoroalkyl ethermoiety;

each of Rb¹ and Rb² is, independently, a sidechain segment including aperfluoroalkyl ether moiety;

each Ri is, independently, a divalent linking segment including afunctional group including elements from Group 13-17 of the periodictable of the elements; and

each of Re¹ and Re² is, independently, a monovalent end segmentincluding a functional group including elements from Group 13-17 of theperiodic table of the elements;

wherein Rb¹≠Rc≠Rb²;

the lubricant having a segment weight average molecular weight (α)determined according to the formula:

α=[molecular weight of Rb¹+molecular weight of Rb²+molecular weight ofRc]÷3; and

a dewetting thickness T_(dw) determined according to the formula:

T _(dw)=ψ(α);

wherein ψ is function determined from a relationship between a dewettingthickness and a segment weight average molecular weight of a pluralityof other lubricants, which may be a linear fit of these data, each ofthe plurality of other lubricants independently including a centersegment and/or sidechain segments including perfluoroalkyl ethermoieties.

It is important to note that in alternative approaches, the lubricantlayer formed on the protective overcoat may include any aspect of thelubricant described herein, singly and/or in any combination.

In various aspects, the lubricant layer can be formed on the magneticrecording medium, specifically on the protective overcoat, via a dipcoating method. For instance, in one aspect the magnetic recordingmedium may be dipped into a lubricant bath including the multidentateperfluoropolyether boundary lubricant according to one or more aspectsof the disclosure and a fluorocarbon solvent such as Vertrel-XF. After apredetermined amount of time, the magnetic recording medium may beremoved from the lubricant bath at a controlled rate. The solvent maythen evaporate, leaving behind a lubricant layer comprising the boundarylubricant according to one aspect of the disclosure. The percentage ofthe lubricant remaining on the surface of the magnetic recording mediumafter disposition of the lubricant may be referred to as the bondedpercentage or the bonding percentage. The bonding percentage may bequantified for various time periods by exposing the lubricated magneticrecording medium with the solvent used in the lubricant bath.

The thickness of the lubricant layer may be tuned by controlling thesubmergence duration of the magnetic recording medium in the lubricantbath, the rate at which the magnetic recording medium is removed fromthe coating solution, and/or the concentration of the boundary lubricantaccording to one or more aspects of the disclosure in the lubricantbath.

In one or more aspects, the concentration of lubricant in the lubricantbath may be in a range from about 0.1 g/L to about 0.2 g/L. In yet otheraspects, the concentration of the lubricant in the lubricant bath may beselected so as to achieve a resulting lubricant layer with a thicknessin a range from about less than or equal to about 3 nanometers (nm), orless than or equal to about 2 nm, or less than or equal to about 1 nm orfrom about 0.3 nm to less than about 1 nm.

It is important to note that formation of the lubricant layer on thesurface of the magnetic recording medium, specifically on the surface ofthe protective overcoat, is not limited to dip coating, but may alsoinvolve spin coating, spray coating, a vapor deposition, combinationsthereof, or any other suitable coating process as would be understood byone having skill in the art upon reading the present disclosure. Inaddition, the magnetic recording layer, the protective overcoat, and/orany of the other layers of the media (e.g., including each of the layersshown for media 200 in FIG. b) may be formed using any of numerousdeposition methods that are known in the art.

It should be noted that methodology presented herein for at least someof the various aspects may be implemented, in whole or in part, incomputer hardware, by hand, using specialty equipment, and/or the like,and combinations thereof.

Moreover, any of the structures and/or steps may be implemented usingknown materials and/or techniques, as would become apparent to oneskilled in the art upon reading the disclosure.

ASPECTS LISTING

Having described the various aspects of the disclosure herein, furtherspecific aspects include those set forth in the following paragraphs:

A1. A lubricant comprising: a plurality of segments, each linkedtogether by ether linkages according to a general formula:

Re¹—Rb¹—Ri—Rc—Ri—Rb²—Re²;

wherein Rc is a divalent center segment including a perfluoroalkyl ethermoiety;

wherein each of Rb¹ and Rb² is, independently, a sidechain segmentincluding a perfluoroalkyl ether moiety;

wherein each Ri is, independently, a divalent linking segment includinga functional group including elements from Group 13-17 of the periodictable of the elements;

wherein each of Re¹ and Re² is, independently, a monovalent end segmentincluding a functional group including elements from Group 13-17 of theperiodic table of the elements;

wherein Rb¹≠Rc≠Rb²; and

wherein the lubricant comprises: a segment weight average molecularweight (α) determined according to the formula:

α=[molecular weight of Rb¹+molecular weight of Rb²+molecular weight ofRc]÷3;

and

wherein a dewetting thickness of the lubricant T_(dw) is determinedaccording to the formula:

T _(dw)=ψ(α);

wherein ψ is a function determined from a relationship between dewettingthickness and segment weight average molecular weight of a plurality ofother lubricants;

wherein each of the plurality of other lubricants includes one or moresegments including perfluoroalkyl ether moieties;

wherein the segment weight average molecular weight of each of the otherlubricants is equal to the weight average molecular weight of the one ormore segments including perfluoroalkyl ether moieties present in therespective other lubricant; and

wherein the segment weight average molecular weight of each of theplurality of other lubricants is from about 300 g/mol to about 5,000g/mol.

A2. The lubricant according to aspect A1, wherein each functional groupincludes: a saturated C₁-C₂₀ radical, an unsaturated C₁-C₂₀ radical, analicyclic C₃-C₂₀ radical, a heterocyclic C₃-C₂₀ radical, an aromaticC₅-C₂₀ radical, a heteroaromatic C₅-C₂₀ radical, a cyclotriphosphazineradical, a halogen, —NR*₂, —NR*—CO—R*, —OR*, —O—CO—R*, —CO—O—R*, —SeR*,—TeR*, —PR*₂, —PO—(OR*)₂, —O—PO—(OR*)₂, —N═P(NR*₂)₃, —AsR*₂, —SR*,—SO₂—(OR*)₂—, —BR*₂, —SiR*₃, —(CH₂)q-SiR*₃, —(CF₂)q-SiR*₃, or acombination thereof, wherein q is 1 to 10 and each R* is, independentlya hydrogen, a halogen, a saturated, unsaturated, aromatic, and/orheterocyclic C₁-C₂₀ radical, and wherein two or more R* may jointogether to form a ring structure, and wherein at least one functionalgroup is selected to be attachable to the protective overcoat of themagnetic recording media.

A3. The lubricant according to aspect A1 or A2, wherein each functionalgroup is a hydroxyl (—OH).

A4. The lubricant according to any one of aspects A1 through A3,including a weight average molecular weight from about 1 to 20kiloDaltons (kDa) and a polydispersity of from about 1 to 2.

A5. The lubricant according to any one of aspects A 1 through A4,wherein Rc includes a perfluoroethyl ether moiety and each of Rb¹ andRb² includes a perfluoroethyl ether moiety.

A6. The lubricant according to any one of aspects A 1 through A5,wherein each Ri has the general formula:

wherein each R¹ is, independently, a functional group including elementsfrom Group 13-17 of the periodic table of the elements.

A7. The lubricant according to any one of aspects A1 through A6, whereinRe¹ has the general formula:

Re² has the general formula:

wherein each R¹ is, independently, a functional group including elementsfrom Group 13-17 of the periodic table of the elements.

A8. The lubricant according to any one of aspects A 1 through A7,wherein:

Rc is of the formula:

Rb¹ is of the formula:

Rb² is of the formula:

wherein each of x, y¹ and y² is, independently, an integer from 1 to 10.

A9. The lubricant according to aspect A8, wherein x is less than y¹ andx is less than y².

A10. The lubricant according to aspect A8, wherein x is greater than y¹and x is greater than y².

A11. The lubricant according to aspect A8, A9, or A10, wherein y¹≠y².

A12. The lubricant according to aspect A8, A9, or A10, wherein y¹=y².

A13. The lubricant according to any one of aspects A6 through A12,wherein each R¹ is a hydroxyl (—OH).

A14. The lubricant according to any one of aspects A1 through A13including the formula:

wherein each of x, y¹, and y² is an integer from 1 to 10; and

y¹≠x≠y².

A15. The lubricant according to any one of aspects A1 through A14,wherein

the dewetting thickness T_(dw) is according to the formula:

T _(dw)=0.0045(α)+8.0226;

wherein α=[molecular weight of Rb¹+molecular weight of Rb²+molecularweight of Rc]÷3.

A16. The lubricant according to any one of aspects A6 through A14,wherein

the dewetting thickness T_(dw) is according to the formula:

T _(dw)=0.0045(α)+8.0226; and

α=(116.015*y ¹+116.015*y ²+116.015*x)÷3.

A17. The lubricant according to any one of aspects A1 through A16,including a weight average molecular weight from about 1 to 20kiloDaltons (kDa) and a polydispersity of from about 1 to 2.

A18. The lubricant according to any one of aspects A1 through A17,including a dewetting thickness of less than or equal to about 3 nm.

A19. A magnetic recording medium, comprising: a magnetic recording layeron a non-magnetic substrate; a protective overcoat on the magneticrecording layer; and a lubricant layer including the lubricant accordingto any one of aspects A1 through A18 on the protective overcoat.

A20. The magnetic recording medium according to aspect A19, wherein thelubricant has a bonding percentage of about 70% to less than 100%.

A21. The magnetic recording medium according to aspect A 19 or A20,wherein an average thickness of the lubricant is less than or equal toabout 3 nanometers.

A22. A method to determine a dewetting thickness of a lubricantaccording to any one of aspects A1 through A18, comprising:

-   a) providing a representation of the lubricant according to the    general formula:

Re¹—Rb¹—Ri—Rc—Ri—Rb²—Re²;

-   b) determining a segment weight average molecular weight (α)    according to the formula:

α=[molecular weight of Rb¹+molecular weight of Rb²+molecular weight ofRc]÷3; and

-   c) determining the dewetting thickness T_(dw) of the lubricant    according to the formula:

T _(dw)=ψ(α);

wherein ψ is a function determined from a relationship between dewettingthickness and segment weight average molecular weight of a plurality ofother lubricants;

wherein each of the plurality of other lubricants includes one or moresegments including perfluoroalkyl ether moieties;

wherein the segment weight average molecular weight of each of the otherlubricants is equal to the weight average molecular weight of the one ormore segments including perfluoroalkyl ether moieties present in therespective other lubricant; and

wherein the segment weight average molecular weight of each of theplurality of other lubricants is from about 300 g/mol to about 5,000g/mol.

A23. A method to determine a dewetting thickness of a lubricant,comprising:

a) providing a representation of the lubricant including a plurality ofsegments, each linked together through an ether linkage according to ageneral formula:

Re¹—Rb¹—Ri—Rc—Ri—Rb²—Re²;

wherein Rc is a divalent center segment including a perfluoroalkyl ethermoiety;

each of Rb¹ and Rb² is, independently, a sidechain segment including aperfluoroalkyl ether moiety;

each Ri is, independently, a divalent linking segment including afunctional group including elements from Group 13-17 of the periodictable of the elements; and

each of Re¹ and Re² is, independently, a monovalent end segmentincluding a functional group including elements from Group 13-17 of theperiodic table of the elements;

wherein Rb¹≠Rc≠Rb²;

b) determining a segment weight average molecular weight (α) accordingto the formula:

α=[molecular weight of Rb¹+molecular weight of Rb²+molecular weight ofRc]÷3; and

c) determining the dewetting thickness T_(dw) of the lubricant accordingto the formula:

T _(dw)=ψ(α);

wherein ψ is a function determined from a relationship between dewettingthickness and segment weight average molecular weight of a plurality ofother lubricants;

wherein each of the plurality of other lubricants includes one or moresegments including perfluoroalkyl ether moieties;

wherein the segment weight average molecular weight of each of the otherlubricants is equal to the weight average molecular weight of the one ormore segments including perfluoroalkyl ether moieties present in therespective other lubricant; and

wherein the segment weight average molecular weight of each of theplurality of other lubricants is from about 300 g/mol to about 5,000g/mol.

A24. The method according to aspect A22 or A23, wherein the dewettingthickness T_(dw) of the lubricant is according to the formula:

T _(dw)=0.0045(α)+8.0226.

A25. The method according to any one of aspects A22 through A24, whereinthe lubricant includes the formula:

wherein each of x, y¹, and y² is an integer from 1 to 10;

y¹≠x≠y²; and

α=(116.015*y¹+116.015*y²+116.015*x)÷3.

A26. The method according to aspect A25 wherein x is less than y¹ and xis less than y².

A27. The method according to aspect A25 wherein x is greater than y¹ andx is greater than y².

A28. The method according to any one of aspects A25 through A27, whereiny¹≠y².

A29. The method according to any one of aspects A25 through A27, whereiny¹=y².

A30. A data storage system, comprising:

at least one magnetic head;

a magnetic recording medium according to any one of aspects A19 throughA21;

a drive mechanism for positioning the at least one magnetic head overthe magnetic recording medium; and

a controller electrically coupled to the at least one magnetic head forcontrolling operation of the at least one magnetic head.

A31. A data storage system, comprising:

a slider comprising at least one magnetic head and an air bearingsurface (ABS), wherein a lubricant according to any one of aspects A1through A18 is disposed on the ABS; and

a magnetic recording medium including a magnetic recording layer;

wherein the slider is configured to write information to the magneticrecording layer using heat assisted magnetic recording (HAMR).

The above description is made for the purpose of illustrating thegeneral principles of the present disclosure and is not meant to limitthe inventive concepts claimed herein. Further, particular featuresdescribed herein can be used in combination with other describedfeatures in each of the various possible combinations and permutations.

It should be noted that in the development of any such actual aspect,numerous implementation-specific decisions must be made to achieve thedeveloper's specific goals, such as compliance with system related andbusiness related constraints, which will vary from one implementation toanother. Moreover, it will be appreciated that such a development effortmight be complex and time consuming but would nevertheless be a routineundertaking for those of ordinary skill in the art having the benefit ofthis disclosure. In addition, the device, system and/or methodused/disclosed herein can also comprise some components other than thosecited.

Unless otherwise specifically defined herein, all terms are to be giventheir broadest possible interpretation including meanings implied fromthe specification as well as meanings understood by those skilled in theart and/or as defined in dictionaries, treatises, and the like.

It must also be noted that, as used in the specification and theappended claims, the singular forms “a,” “an” and “the” include pluralreferents unless otherwise specified.

As also used herein, the term “about” denotes an interval of accuracythat ensures the technical effect of the feature in question. In variousapproaches, the term “about” when combined with a value, refers to plusand minus 10% of the reference value. For example, a thickness of about10 angstroms (Å) refers to a thickness of 10 Å+/−1 Å, e.g., from 0.9 Åto 1.1 Å in this example.

In the summary and this detailed description, each numerical valueshould be read once as modified by the term “about” (unless alreadyexpressly so modified), and then read again as not so modified unlessotherwise indicated in context. Also, in the summary and this detaileddescription, it should be understood that a physical range listed ordescribed as being useful, suitable, or the like, is intended that anyand every value within the range, including the end points, is to beconsidered as having been stated. For example, “a range of from 1 to 10”is to be read as indicating each and every possible number along thecontinuum between about 1 and about 10. Thus, even if specific datapoints within the range, or even no data points within the range, areexplicitly identified or refer to only a few specific, it is to beunderstood that inventors appreciate and understand that any and alldata points within the range are to be considered to have beenspecified, and that inventors possessed knowledge of the entire rangeand all points within the range.

As used in the specification and claims, “near” is inclusive of “at.”The term “and/or” refers to both the inclusive “and” case and theexclusive “or” case, and such term is used herein for brevity. Forexample, a composition comprising “A and/or B” may comprise A alone, Balone, or both A and B.

Various components described in this specification may be described as“including” and/or made of, and/or “having” certain materials,properties, or compositions of material(s). In one aspect, this can meanthat the component consists of certain materials, properties, orcompositions of materials. In another aspect, this can mean that thecomponent comprises certain materials, properties, or compositions ofmaterial(s).

The word “exemplary” is used herein to mean “serving as an example,instance, or illustration.” Any implementation or aspect describedherein as “exemplary” is not necessarily to be construed as preferred oradvantageous over other aspects of the disclosure. Likewise, the term“aspects” does not require that all aspects of the disclosure includethe discussed feature, advantage or mode of operation. The term“coupled” is used herein to refer to the direct or indirect couplingbetween two objects. For example, if object A physically touches objectB, and object B touches object C, then objects A and C may still beconsidered coupled to one another-even if they do not directlyphysically touch each other.

It is further noted that the term “over” and/or the term “on” as used inthe disclosure in the context of one component located over anothercomponent, or in the context of one component located on anothercomponent, may be used to mean a component that is directly on a surfaceof another component e.g., disposed in physical contact with the surfaceof the other component, and/or in another component, e.g., directlyembedded in a component. Thus, for example, a first component that isover or on the second component may mean that (1) the first component islocated over or above the second component, but not directly touchingthe second component, (2) the first component is directly on (e.g.,directly on a surface of) the second component, and/or (3) the firstcomponent is in (e.g., embedded in) the second component.

In the disclosure various ranges in values may be specified, describedand/or claimed. It is noted that any time a range is specified,described and/or claimed in the specification and/or claim, it is meantto include the endpoints (at least in one aspect). In another aspect,the range may not include the endpoints of the range. In the disclosurevarious values (e.g., value X) may be specified, described and/orclaimed. In one aspect, it should be understood that the value X may beexactly equal to X. In one aspect, it should be understood that thevalue X may be “about X,” with the meaning noted above. Likewise, when avalue is determined according to an equation, it is to be understoodthat in one aspect, the value is equal to the value calculated accordingto the equation and in another aspect, the value is about equal to thevalue calculated according to the equation according to the meaningnoted above, or as is expressly provided for, e.g., plus or minus (+/−)a specific amount.

While various aspects have been described above, it should be understoodthat they have been presented by way of example only, and notlimitation. Thus, the breadth and scope of an aspect of the presentinvention should not be limited by any of the above-described exemplaryaspects, but should be defined only in accordance with the followingclaims and their equivalents.

What is claimed is:
 1. A lubricant comprising: a plurality of segments,each linked together by ether linkages according to a general formula:Re¹—Rb¹—Ri—Rc—Ri—Rb²—Re²; wherein Rc is a divalent center segmentincluding a perfluoroalkyl ether moiety; wherein each of Rb¹ and Rb² is,independently, a sidechain segment including a perfluoroalkyl ethermoiety; wherein each Ri is, independently, a divalent linking segmentincluding a functional group including elements from Group 13-17 of theperiodic table of the elements; wherein each of Re¹ and Re² is,independently, a monovalent end segment including a functional groupincluding elements from Group 13-17 of the periodic table of theelements; wherein Rb¹≠Rc≠Rb²; and wherein the lubricant comprises: asegment weight average molecular weight (α) determined according to theformula:α=[molecular weight of Rb¹+molecular weight of Rb²+molecular weight ofRc]÷3; and wherein a dewetting thickness of the lubricant T_(dw) isdetermined according to the formula:T _(dw)=ψ(α); wherein ψ is a function determined from a relationshipbetween a dewetting thickness and a segment weight average molecularweight of a plurality of other lubricants; wherein each of the pluralityof other lubricants includes one or more segments includingperfluoroalkyl ether moieties; wherein the segment weight averagemolecular weight of each of the other lubricants is equal to a weightaverage molecular weight of the one or more segments includingperfluoroalkyl ether moieties present in the respective other lubricant;and wherein the segment weight average molecular weight of each of theplurality of other lubricants is from about 300 g/mol to about 5,000g/mol.
 2. The lubricant of claim 1, wherein each functional groupincludes: a saturated C₁-C₂₀ radical, an unsaturated C₁-C₂₀ radical, analicyclic C₃-C₂₀ radical, a heterocyclic C₃-C₂₀ radical, an aromaticC₅-C₂₀ radical, a heteroaromatic C₅-C₂₀ radical, a cyclotriphosphazineradical, a halogen, —NR*₂, —NR*—CO—R*, —OR*, —O—CO—R*, —CO—O—R*, —SeR*,—TeR*, —PR*₂, —PO—(OR*)₂, —O—PO—(OR*)₂, —N═P(NR*₂)₃, —AsR*₂, —SR*,—SO₂—(OR*)₂, —BR*₂, —SiR*₃, —(CH₂)q-SiR*₃, —(CF₂)q-SiR*₃, or acombination thereof, wherein q is 1 to 10 and each R* is, independently,a hydrogen, a halogen, a saturated, unsaturated, aromatic, and/orheterocyclic C₁-C₂₀ radical, and wherein two or more R* may jointogether to form a ring structure, and wherein at least one functionalgroup is selected to be attachable to a protective overcoat of amagnetic recording media comprising the lubricant.
 3. The lubricant ofclaim 1, wherein each functional group is a hydroxyl (—OH).
 4. Thelubricant of claim 1, comprising a weight average molecular weight fromabout 1 to 20 kiloDaltons (kDa) and a polydispersity from about 1 to 2.5. The lubricant of claim 1, comprising a dewetting thickness of lessthan or equal to about 3 nanometers.
 6. The lubricant of claim 1,wherein: Rc includes a perfluoroethyl ether moiety; each of Rb¹ and Rb²includes a perfluoroethyl ether moiety; each Ri has the general formula:

Re¹ has the general formula:

and Re² has the general formula:

wherein each R¹ is, independently, a functional group including elementsfrom Group 13-17 of the periodic table of the elements.
 7. The lubricantof claim 6, wherein: Rc is of the formula:

Rb¹ is of the formula:

and Rb² is of the formula:

and wherein each of x, y¹ and y² is, independently, an integer from 1 to10.
 8. The lubricant of claim 7, comprising a weight average molecularweight from about 1 to 20 kiloDaltons (kDa) and a polydispersity fromabout 1 to
 2. 9. The lubricant of claim 7, wherein x is less than y¹ andx is less than y².
 10. The lubricant of claim 7, wherein x is greaterthan y¹ and x is greater than y².
 11. The lubricant of claim 7, whereiny¹≠y².
 12. The lubricant of claim 7, wherein each R¹ is a hydroxyl(—OH).
 13. The lubricant of claim 1, according to the formula:

wherein each of x, y¹, and y² is an integer from 1 to 10; and whereiny¹≠x≠y².
 14. The lubricant of claim 13: wherein the dewetting thicknessT_(dw)=0.0045(α)+8.0226; and whereinα=(116.015*y¹+116.015*y²+116.015*x)÷3.
 15. A data storage system,comprising: at least one magnetic head; a magnetic recording mediumincluding a lubricant according to claim 1; a drive mechanism forpositioning the at least one magnetic head over the magnetic recordingmedium; and a controller electrically coupled to the at least onemagnetic head for controlling operation of the at least one magnetichead.
 16. A data storage system, comprising: a slider comprising atleast one magnetic head and an air bearing surface (ABS), wherein alubricant according to claim 1 is disposed on the ABS; and a magneticrecording medium including a magnetic recording layer; wherein theslider is configured to write information to the magnetic recordinglayer using heat assisted magnetic recording (HAMR).
 17. A magneticrecording medium, comprising: a magnetic recording layer on a substrate;a protective overcoat on the magnetic recording layer; and a lubricantlayer comprising the lubricant according to claim 1 on the protectiveovercoat.
 18. The magnetic recording medium of claim 17, wherein thelubricant has a bonding percentage of about 70% to less than 100%. 19.The magnetic recording medium of claim 17, wherein an average thicknessof the lubricant is less than or equal to about 3 nanometers.
 20. Alubricant comprising a plurality of segments linked together by etherlinkages according to a formula:

wherein each of x, y¹, and y² is an integer from 1 to 10; whereiny¹≠x≠y²; and comprising a dewetting thickness T_(dw)=0.0045(α)+8.0226;wherein α=(116.015*y¹+116.015*y²+116.015*x)÷3.
 21. The lubricant ofclaim 20 comprising a weight average molecular weight from about 1 to 20kiloDaltons (kDa) and a polydispersity from about 1 to
 2. 22. A methodto determine a dewetting thickness of a lubricant, comprising: a)generating a chemical representation of the lubricant including aplurality of segments, each linked together through an ether linkageaccording to a general formula:Re¹—Rb¹—Ri—Rc—Ri—Rb²—Re²; wherein Rc is a divalent center segmentincluding a perfluoroalkyl ether moiety; wherein each of Rb¹ and Rb² is,independently, a sidechain segment including a perfluoroalkyl ethermoiety; wherein each Ri is, independently, a divalent linking segmentincluding a functional group including elements from Group 13-17 of theperiodic table of the elements; wherein each of Re¹ and Re² is,independently, a monovalent end segment including a functional groupincluding elements from Group 13-17 of the periodic table of theelements; and wherein Rb¹≠Rc≠Rb²; b) determining a segment weightaverage molecular weight (α) according to the formula:α=[molecular weight of Rb¹+molecular weight of Rb²+molecular weight ofRc]÷3; and c) determining the dewetting thickness T_(dw) of thelubricant according to the formula:T _(dw)=0.0045(α)+8.0226.
 23. The method of claim 22, wherein thelubricant includes a compound with the formula:

wherein each of x, y¹, and y² is an integer from 1 to 10; whereiny¹≠x≠y²; and wherein α=(116.015*y¹+116.015*y²+116.015*x)÷3.
 24. Themethod of claim 23, wherein x is less than y¹ and x is less than y². 25.The method of claim 23, wherein y¹≠y².